The present invention relates generally to isolation systems used to support and protect sensitive equipment installed on an aircraft, ship, or submarine and more particularly to an isolation system that protects such equipment against shock and vibration and also minimizes the transmission of acoustic energy from the isolated equipment to the supporting structure.
Traditionally, the U.S. Government and other governments have required that electronic equipment and other sensitive equipment used aboard military vessels, such as aircraft, ships, and submarines, be specifically designed and manufactured so as to withstand these vessels"" challenging operational environments. Accordingly, suppliers have been required to specially xe2x80x9cruggedizexe2x80x9d or xe2x80x9cmilitarizexe2x80x9d equipment in order to satisfy certain testing criteria, such as shock testing and/or vibration testing.
Unfortunately, such militarized equipment has two significant drawbacks. First, specially designing each piece of equipment to withstand challenging operational environments can impose significant costs. Second, because each piece of equipment must be specially designed to meet testing criteria, the deployment of state-of-the-art technologies can be significantly delayed. For instance, an improved flat screen display technology may be readily available for commercial applications, but it may be years before the technology can be incorporated into military equipment.
As a result of these and other drawbacks of so-called xe2x80x9cMIL-SPECxe2x80x9d equipment, since the early 1990""s the Department of Defense has issued various directives permitting and, in fact, encouraging, utilization of so-called xe2x80x9ccommercial-off-the-shelfxe2x80x9d (COTS) technology. As a result, military vessels have been increasingly using COTS electronic components and systems in lieu of militarized equipment. COTS equipment is cheaper, it offers the latest technology, and in many instances, it offers a larger pool of suppliers from which the Government (or its prime contractors) can select.
One challenge presented by COTS equipment, however, relates to its ability to pass shock and vibration requirements. Militarized equipment has traditionally been rigidly mounted to shipboard structures. However, COTS equipment tends to have limited capabilities to withstand shock and vibration motions, and, therefore, tends to be unsuitable for being rigidly mounted to shipboard structures. Therefore, COTS equipment usually requires isolation devices (shock mounts) to mitigate the effects of shock and vibration presented in the operational environment. For example, COTS equipment is often placed in component racks that are coupled to a vessel structure (e.g., a floor or a wall) via one or more shock absorption mounts. Alternatively, individual pieces of equipment may be coupled directly to the vessel structure via shock absorption mounts. In other instances, COTS equipment may be placed on flat platforms that, in turn, are coupled to the vessel structure using shock absorption mounts.
The design of the shock absorption mounts used to protect COTS equipment runs into the inherent difficulty of designing into a single isolator the ability to perform equally well as a shock isolator and a vibration isolator. This problem arises due to the fact that a good vibration isolator tends to be a poor shock isolator and a good vibration isolator tends to be a poor shock isolator. Most attempts to solve the combined isolation problem with a passive device have met with limited success, particularly in shipboard isolation applications where many inputs are often present simultaneously. The typical approach to solving the shipboard isolation problem involves the use of a combination of separate passive isolators for shock and vibration. This inevitably leads to modifying vibration isolators to survive shock inputs and/or modifying shock isolators to perform adequately as vibration isolators. Other environments present similar design difficulties.
Another problem presented to the designer is that the damping mechanism used in a shock isolation system must provide a force that is matched to the mass of the equipment being isolated. When equipment is changed out or modified, the isolation system must be changed to reflect changes in mass and mass distribution. Given the frequency of equipment change-out and upgrades, this is a significant drawback.
The present invention provides an ideal solution in the form of a single self-contained isolation system that provides both effective vibration isolation in the 10 to 200 Hz range and shock isolation from a variety of inputs such as underwater explosions, wave slap, impact, etc. The system also provides acoustic isolation of the base structure to which sensitive equipment is mounted.
An embodiment of the present invention provides a shock and vibration isolation system for mounting equipment to a base wall. The system comprises a load plate configured for attachment of the equipment thereto and a base plate configured for attachment to the base wall. The base plate is substantially parallel to the load plate with a spring arrangement disposed intermediate the load plate and the base plate. The spring arrangement engages the load plate and the base plate to bias the load plate and the base plate in a separated relationship. The system also comprises a damping arrangement disposed intermediate the load plate and the base plate. The damping arrangement is adapted for providing a selectively variable reaction force to the load plate and the base plate responsive to a relative displacement of the load plate with respect to the base plate.
The damping arrangement of an isolation system embodiment according to the present invention may include at least one semi-active damper operatively connected to the base plate and the load plate. The at least one semi-active damper may be a magnetorheological fluid or an electrorheological fluid damper. The damping arrangement may further include a damper controller operatively connected to the at least one semi-active damper for controlling the reaction force applied to the load plate and the base plate.
The damper controller may include an optimum damper force determination module configured for determining from real time data the relative displacement of the load plate and a relative velocity of the load plate with respect to the base plate. The damper controller may also be configured for determining an optimum reaction force based on the relative displacement and relative velocity. The controller may include a current driver operatively connected to the at least one semi-active damper for selectively supplying current to energize the at least one semi-active damper. The controller may include a damper force control module in communication with the optimum force determination module and the current driver.
The damper force control module may be adapted for controlling the supply of current to the at least one semi-active damper according to a predetermined control algorithm. The control algorithm may be selected from the group consisting of clipped optimal control, Lyapunov stability theory, decentralized bang-bang control, and modulated homogeneous friction control.
The optimum reaction force determination module of an isolation system embodiment of the invention may comprise a programmable digital processor having optimum force determination software configured for calculating the optimum reaction force using a set of one or more adjustable gains. The programmable digital processor may also have gain adjustment software configured for determining a mass of the equipment based on the relative displacement and for adjusting the set of one or more adjustable gains based on the determined mass. The optimum force determination module may comprise field replaceable analog circuitry adapted for providing the optimum reaction force.
The spring arrangement of an isolation system embodiment according to the invention may have a natural frequency in a range from about 1.0 Hz. to about 10 Hz. Also, the spring arrangement of an isolation system embodiment may include at least one pneumatic spring.
According to one aspect of the invention, the damping arrangement of a shock and vibration isolation system may include a power supply operatively connected to the at least one semi-active damper. The power supply may be included in the damper controller. In a particular aspect of the invention, the power supply may be rechargeable and the system may further comprise a recharging arrangement in electrical communication with the rechargeable power supply. The recharging arrangement may be attached to one of the base plate and the load plate and may have means for converting vibratory motion to electrical energy for storage in the rechargeable power supply. The means for converting may include an electrical coil, at least one spring and a magnet connected to the at least one spring. The magnet is disposed within the electrical coil so that oscillation of the magnet produces a current in the electrical coil.
Other objects and advantages of the invention will be apparent to one of ordinary skill in the art upon reviewing the detailed description of the invention.